Recently, a voltage-to-digital converting circuit is widely employed as a signal converting circuit, which receives an external voltage of which the magnitude varies to convert the voltage having the magnitude to digital data.
FIG. 1 illustrates the configuration of a conventional voltage-to-digital converting circuit. Referring to FIG. 1, the conventional voltage-to-digital converting circuit 2 includes a voltage generation unit 3, a signal amplification unit 4, and an A/D converter 5.
In this case, a sensor 1 varies the magnitude of its output voltage depending on the external stimulus strength to apply it to the voltage-to-digital converting circuit 2.
The voltage generation unit 3 receives an external voltage (not shown) to generate operating voltages Vdd1 and Vdd2 having voltage levels required for operations of the signal amplification unit 4 and the A/D converter 5.
The signal amplification unit 4 receives the operating voltage Vdd1 from the voltage generation unit 3, amplifies a voltage V1 of the sensor 1, and enables the A/D converter 5 to correctly recognize the magnitude of the amplified voltage V0.
The A/D converter 5 divides a voltage level range of the operating voltage Vdd2 supplied from the voltage generation unit 3 into predetermined units, recognizes the voltage level range corresponding to the magnitude of the output voltage V0 of the signal amplification unit 4, and generates digital data (e.g., a binary code) having a value corresponding to the recognized voltage level range.
The conventional voltage-to-digital converting circuit as described above may be connected to various sensors which vary the magnitude of the output voltage depending on the external stimulus strength to convert an electrical signal of the sensor to digital data, so that the voltage-to-digital converting circuit may be widely applied in various fields.
For example, the voltage-to-digital converting circuit of FIG. 1 may be connected to the sensor 1 which is composed of a sound pressure sensing element MIC for varying an electrostatic capacitance Csen depending on sound pressure generated by an external tone generator, and a bias resistor Rbias connected between a bias voltage Vbias and the sound pressure sensing element MIC to generate an output voltage V1 corresponding to the varied electrostatic capacitance Csen as shown in FIG. 2, so that the voltage-to-digital converting circuit may be applied as a microphone circuit.
Next, operations of the microphone circuit will be described with reference to FIG. 2.
The sound pressure sensing element MIC of the sensor 1 varies the electrostatic capacitance Csen depending on the sound pressure generated by the external tone generator. Accordingly, a current Im flowing through the sound pressure sensing element MIC varies according to a formula such as bias voltage Vbias×varied electrostatic capacitance DCsen of the sound pressure sensing element MIC, so that an input voltage V1 of the voltage-to-digital converting circuit also varies its magnitude according to a formula such as current Im×bias resistance Rbias.
The signal amplification unit 4 then amplifies the input voltage V1 of the sensor 1 by a predetermined magnitude, and the A/D converter 5 generates digital data (e.g., binary code) having a value corresponding to the voltage level of the amplified input voltage V1.
That is, in the microphone circuit of FIG. 2, the sensor 1 varies the magnitude of the voltage depending on the sound pressure of the tone generator, and the voltage-to-digital converting circuit generates digital data having the value corresponding to the voltage magnitude of the sensor 1.
As such, the conventional voltage-to-digital converting circuit performs the signal converting operation on the basis of the voltage to convert the input voltage to digital data.
However, the signal amplification unit 4 of the conventional voltage-to-digital converting circuit must be supplied from the voltage generation unit 3 with an operating voltage having a sufficient magnitude to amplify the A/D converter 5 to recognize the voltage V1 of the sensor 1. Further, the A/D converter 5 must be supplied from the voltage generation unit 3 with an operating voltage having a sufficient magnitude to correctly recognize and divide the output voltage V1 of the sensor 1.
However, the magnitude of the voltage capable of being generated by the voltage generation unit 3 is proportional to the device size and voltage generation capacity of the voltage generation unit 3, so that the voltage generation unit 3 must secure the voltage generation capacity and the size corresponding to the voltage having a sufficient magnitude and capable of being generated by the voltage generation unit 3.
As a result, when the size of the voltage-to-digital converting circuit is applied to a highly integrated System-on-the-Chip (SoC) requiring a fine process and reduced to cause the voltage generation unit 3 not to have the voltage generation capacity and the size for generating the voltage having the sufficient magnitude, the voltage generation unit 3 could not generate the voltage having the magnitude required by the voltage-to-digital converting circuit.
Accordingly, when the conventional voltage-to-digital converting circuit is applied to the highly integrated SoC, the voltage generation unit 3 may not generate the voltage having the sufficient magnitude and capacity, so that performance of the voltage-to-digital converting circuit may be rapidly degraded, and mis-operation may occur in the voltage-to-digital converting circuit in the worst case.
That is, the conventional voltage-to-digital converting circuit is implemented with an analog circuit having a relatively big size (in particular, the voltage generation circuit), so that it is difficult to apply the voltage-to-digital converting circuit to a highly integrated circuit such as the SoC. In addition, operational performance of the voltage-to-digital converting circuit is very susceptible to external noises due to the property of the analog circuit.